Since we as a human race are 'social animals,' as described by John Locke, living with just two people in the world would be the epitome of a mundane existence. Let's also review how marriages and most relationships turn out - for some reason, there are always squabbles, and there are friends or places to console after squabbling with your signifant other. With nobody else in the world, who are you to confide in besides the person you're not exactly agreeing with at that time?

I would despise living with just one other person in existence for the rest of my life. With seven billion other people, I could find another person to love.

tl;dr - I would choose to spare the lives of the rest of the population of the world.